Punctuated Equilibrium
An evolutionary theory stating that sexually reproducing species evolve through long periods of stasis (stability with little change) punctuated by relatively brief periods of rapid speciation.
Punctuated equilibrium theory directly challenges the traditional phyletic gradualism theory, which suggests that species evolve gradually over very long periods across generations.
Modern evolutionary biology accepts both phyletic gradualism and punctuated equilibrium, recognizing that their differences largely depend on the timescale being considered.